Practice question

Understanding CMC highlights phase behavior of amphiphiles. At subsaturation detergent monomers exist dissolved in aqueous phase hydration shell disordered, partial insertion into outer leaflet may increase permeability but leaves bilayer structure largely intact. When monomer concentration reaches thermodynamic threshold where entropic cost of ordering water around hydrophobic tails outweighs micellization free energy, spontaneous aggregation into micelles occurs with hydrocarbon tails sequestered interior and polar heads facing water forming spherical or ellipsoidal particles thirty to fifty angstroms diameter. Below this point no micelles detected by dye solubilization, surface tension or NMR; membranes not disrupted into mixed micelles, so integral proteins remain embedded and organelle barriers persist demonstrated by retention of luminal markers. This intentional sub-CMC usage allows delivery of hydrophobic drugs or limited permeabilization. For complete lysis and purification supra-CMC concentrations mandatory providing sufficient micelles to sequester phospholipids and proteins into soluble particles preventing aggregation and inactivation during biochemical isolation. Experimental determination of CMC using light scattering fluorescent probes ANS or N-phenyl naphthylamine tracks abrupt intensity increase indicating micellization.